73 L48 thermostat change
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Joined: Feb 2002
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From: ATLANTIC HIGHLANDS NJ
73 L48 thermostat change
73 L48. No drain plug on my car, all original. Can I get away with pulling thermostat housing and not lose much fluid?
Don't think it's ever been off, 38k mile car. Think factory had a 198 thermostat, or should i just do a 180.
DRC
Don't think it's ever been off, 38k mile car. Think factory had a 198 thermostat, or should i just do a 180.
DRC
1967 Pedal Car Champion
Joined: Mar 2020
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From: US-PNW
https://www.gm.com/heritage/archive/...formation-kits
According to the doc, the thermostat should be opening at 192°-198°F, which sounds like a 195°. I'd go with what GM recommended though a 180°F isn't going to damage anything. The higher operating temps helped to meet emission requirements. A tip to help bleed off air is to drill a small hole (~1/8") in the flange next to the thermostatic mechanism. This allows the trapped air to escape the block before the t-stat opens.
Even if you did have a drain on your radiator, I'd not touch it! They are susceptible to seizing from corrosion and will just snap off if forced. Yes, you can just pull the upper hose and lose maybe a pint or so of coolant. Might be a good time to remove the lower hose too and do a system flush. Make sure you thoroughly hose down any coolant from the driveway - animals like to lick it because it's sweet but it's highly poisonous and will kill them with kidney failure.
Last edited by barkingrats; Nov 19, 2023 at 10:48 AM.
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Joined: Feb 2002
Posts: 734
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From: ATLANTIC HIGHLANDS NJ
If you have not downloaded the free 1973 specs doc from GM Heritage, I highly recommend it.
https://www.gm.com/heritage/archive/...formation-kits
According to the doc, the thermostat should be opening at 192°-198°F, which sounds like a 195°. I'd go with what GM recommended though a 180°F isn't going to damage anything. The higher operating temps helped to meet emission requirements. A tip to help bleed off air is to drill a small hole (~1/8") in the flange next to the thermostatic mechanism. This allows the trapped air to escape the block before the t-stat opens.
Even if you did have a drain on your radiator, I'd not touch it! They are susceptible to seizing from corrosion and will just snap off if forced. Yes, you can just pull the upper hose and lose maybe a pint or so of coolant. Might be a good time to remove the lower hose too and do a system flush. Make sure you thoroughly hose down any coolant from the driveway - animals like to lick it because it's sweet but it's highly poisonous and will kill them with kidney failure.
https://www.gm.com/heritage/archive/...formation-kits
According to the doc, the thermostat should be opening at 192°-198°F, which sounds like a 195°. I'd go with what GM recommended though a 180°F isn't going to damage anything. The higher operating temps helped to meet emission requirements. A tip to help bleed off air is to drill a small hole (~1/8") in the flange next to the thermostatic mechanism. This allows the trapped air to escape the block before the t-stat opens.
Even if you did have a drain on your radiator, I'd not touch it! They are susceptible to seizing from corrosion and will just snap off if forced. Yes, you can just pull the upper hose and lose maybe a pint or so of coolant. Might be a good time to remove the lower hose too and do a system flush. Make sure you thoroughly hose down any coolant from the driveway - animals like to lick it because it's sweet but it's highly poisonous and will kill them with kidney failure.
Funny thing is I just had NCRS judging, Top Flight award. One thermostat housing bolt had wrong head marking. So removed one bolt to correct that and now a slight leak. So have to put in new gasket.
As everything ran perfect I may just put the current thermostat back in.
Tks. DRC
Race Director
Joined: Sep 2001
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From: Wellington, FL
St. Jude Donor '11 thru '25
I've done this job a few times and did so by first using suction and removing about a gallon of coolant by inserting a piece of clear plastic hose in the radiator, 1/4 inch inside diameter or so. This will allow you to replace the stat w/o problems with coolant leakage. When finished, just reinstall the coolant. Piece of cake...
Last edited by Jud Chapin; Nov 19, 2023 at 12:13 PM.
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I've done it more than once without draining any antifreeze.
I just wrap an old towel around the housing to pick up the fluid which isn't that much...
I just wrap an old towel around the housing to pick up the fluid which isn't that much...
Tech Contributor
Joined: Aug 1999
Posts: 14,384
Likes: 6,408
From: At my Bar drinking and wrenching in Lafayette Colorado
The factory used the 195 thermostats for a good reason. The engine actually operates more efficiently at higher temperatures (it's a heat engine), so the 180-degree thermostat will gain you no advantage. Remember: The thermostat has no control over the maximum temperature of the engine. The thermostat only controls minimum temperature. If you have a temperature problem with the engine running hot, switching from a 195 to a 180 will do absolutely nothing to change the issue (unless the thermostat is defective).
As a side note to put this in perspective, one of the ways the NASCAR engine builders get so much power out of their engines is that they run the coolant temperature at 260-280 degrees (cooling system pressure up to 33 psi). And we see Corvette owners who go into panic mode when water temp hits 210-215...
Lars
As a side note to put this in perspective, one of the ways the NASCAR engine builders get so much power out of their engines is that they run the coolant temperature at 260-280 degrees (cooling system pressure up to 33 psi). And we see Corvette owners who go into panic mode when water temp hits 210-215...
Lars
Thread Starter
Pro
Joined: Feb 2002
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From: ATLANTIC HIGHLANDS NJ
The factory used the 195 thermostats for a good reason. The engine actually operates more efficiently at higher temperatures (it's a heat engine), so the 180-degree thermostat will gain you no advantage. Remember: The thermostat has no control over the maximum temperature of the engine. The thermostat only controls minimum temperature. If you have a temperature problem with the engine running hot, switching from a 195 to a 180 will do absolutely nothing to change the issue (unless the thermostat is defective).
As a side note to put this in perspective, one of the ways the NASCAR engine builders get so much power out of their engines is that they run the coolant temperature at 260-280 degrees (cooling system pressure up to 33 psi). And we see Corvette owners who go into panic mode when water temp hits 210-215...
Lars
As a side note to put this in perspective, one of the ways the NASCAR engine builders get so much power out of their engines is that they run the coolant temperature at 260-280 degrees (cooling system pressure up to 33 psi). And we see Corvette owners who go into panic mode when water temp hits 210-215...
Lars
And, car runs not hot at all. In Summer idling and checking with the IR Gun water neck, hoses, etc. show around 180.
Engine is as it left the factory. Except for lighter springs in distributor for 36 @ around 2,800.
DRC
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Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
While I agree with the thermo aspects of higher temps being more efficient........on a stock 350 in a C3 the elevated temps along with the hot heat riser port cooking things up for you....this is not a good idea.......you want some Vapor Lock? J
The other thing is NASCAR is not driving in traffic.......traffic raises underhood temps and intake air intake temps......
In the real world....cooler is better...to a point......
I like to see 170-190 depending on application.......
The LS argument of all of them running 210 is not valid because the LS engine has a plastic intake.......and perfect real time tuning.......
Jebby
The other thing is NASCAR is not driving in traffic.......traffic raises underhood temps and intake air intake temps......
In the real world....cooler is better...to a point......
I like to see 170-190 depending on application.......
The LS argument of all of them running 210 is not valid because the LS engine has a plastic intake.......and perfect real time tuning.......
Jebby
Thread Starter
Pro
Joined: Feb 2002
Posts: 734
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From: ATLANTIC HIGHLANDS NJ
While I agree with the thermo aspects of higher temps being more efficient........on a stock 350 in a C3 the elevated temps along with the hot heat riser port cooking things up for you....this is not a good idea.......you want some Vapor Lock? J
The other thing is NASCAR is not driving in traffic.......traffic raises underhood temps and intake air intake temps......
In the real world....cooler is better...to a point......
I like to see 170-190 depending on application.......
The LS argument of all of them running 210 is not valid because the LS engine has a plastic intake.......and perfect real time tuning.......
Jebby
The other thing is NASCAR is not driving in traffic.......traffic raises underhood temps and intake air intake temps......
In the real world....cooler is better...to a point......
I like to see 170-190 depending on application.......
The LS argument of all of them running 210 is not valid because the LS engine has a plastic intake.......and perfect real time tuning.......
Jebby
DRC
Melting Slicks
Joined: May 2021
Posts: 2,287
Likes: 1,327
From: Fleming Island, FL
I may be overthinking this but I went with a 180 thermostat over the 195 is for under the hood temperature and ever feel the "made out of plastic" hood after a long drive!!
The main reason Cup cars runs such high temperatures is because the opening to the radiator is so small, like the size of a pack of cigarettes to reduce drag. The high pressure cooling system came about when NASCAR limited the cooling system capacity to 2 gallons max.
The main reason Cup cars runs such high temperatures is because the opening to the radiator is so small, like the size of a pack of cigarettes to reduce drag. The high pressure cooling system came about when NASCAR limited the cooling system capacity to 2 gallons max.
